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Showing posts from July, 2013

Why I don't use Cycle Time in Kanban

Why I don't use cycle time in Kanban from Andy Carmichael

These slides were produced in response to a request for a brief summary of the terms I use for describing flow systems, particularly in a Kanban context. Along the same theme also see The difference between Cycle Time and Lead TimeMore Musings on Little's LawVisual explanation of Kanban terms and In search of unambiguous terminology for Flow systems.

What is there to be afraid of?

What is worthy of our fear? Is Death? Surely not. He who lives will die, and such inevitability must be respected and known, yet not cause dread. No more fear taxes, since he who earns can scarce keep it all, can he, any more than he can take it with him? For what purpose would you keep it all? I grant you death and taxes should be avoided - where it's possible to do so with honesty and honour. But they are not worthy of our fear.

Maybe boredom is a more suitable object. To live an uninteresting life is both eminently possible and profoundly fearful. Don't you have a mind though, and doesn't it engender imagination? And is it beyond that imagination to find an action, project or enterprise that could engage you in some means of improving your own or your fellow's lot? Boredom is not worthy of fear, since it is easily remedied.

Yet I think there is an entity worthy of fear, fear true and cold. It is waste... the waste of human potential. Such waste inhabits every corner…

More Musings on Little's Law

My previous posting about why not  to use Cycle Time in Kanban resulted in some interesting discussions, and I'm grateful to +Steve Tendon for pointing me in the direction of this paper [1] by John D.C. Little and Stephen C. Graves which gives some very helpful historical background into the derivation of Little's Law, its applicability and some of the terminology used.

Little's own formulation of the "law" was as follows:



L = average number of items in the queuing system,
(equivalent to WIP in Kanban terminology)

W = average waiting time in the system for an item,
(equivalent to System Lead Time)

λ = average number of items arriving per unit time
(equivalent to Delivery Rate, assuming "stationarity")

With Kanban preferred terms we can see this maps to:

WIP =  Delivery Rate * Lead Time
Delivery Rate = WIP / Lead Time

Little used "waiting time" for the time taken by one unit to traverse the system (W) because his original context w…

The difference between Cycle Time and Lead Time... and why not to use Cycle Time in Kanban

Before addressing the question of which terms you should use in the Kanban method, let me attempt an explanation of the generally accepted meaning of these terms. (We'll come to the question of how generally later!)

Firstly Cycle Time: it is the time between units emerging from a process. You could visualise it like this:

Our system here could be a Development Team say, and the units User Stories (although we would expect to have more variation in this case). Equally it could be a bicycle assembly plant (working not very fast). The Cycle Time here is half a day because the system produces one unit every 0.5 days. Therefore the Delivery Rate (which is Kanban's preferred term for measuring throughput) is 2 units per day.

To understand Lead Time we need to put a marker on one of the items entering the process, and then see how long before that particular item emerges. Like this:

Lead Time is the time taken for one unit to pass through the process…